The situation is, the taxpayers did not file FBARs going back to 2014 as they did not know they had to. There was no unreported income. They are gathering the information and the FBARs will be filed.
Form 8938 was missed in 2019 and possibly in 2018 and 2014. Schedule B was either omitted or the questions in Part III not answered correctly. We do not yet have full data for all the years.
My question is, how far back to amend income tax returns to include Schedule B and the 8938's, if needed?
I have had multiple of these. In EVERY time I have worked with a tax attorney to get the client up-to-date. Why, because this starts with the Criminal Division, not the Civil. There used to be a streamlined provision that the penalties could be reduced. See https://www.irs.gov/individuals/international-taxpayers/delinquent-fbar-submission-procedures but the IRs requests 3 years of amended returns and 6 years of FBAR's. There is too much at risk (malpractice wise) for you not to consult a tax attorney on this.